Typically glazed roofs are assembled on-site. The walls, supporting posts, rafters and beams are assembled to form a complete conservatory roof and enclosed structure. The beam rafters and panels of the glazed roof are then assembled at the job site.
On-site construction is problematic simply because it is very labor intensive and requires a great deal of time to ensure that everything is properly installed to prevent leakage and other like problems. Even with relative small roofs, such as a bay window roof, on-site fabrication is required and can be expensive due to the labor costs.